Performing a scaling process on data for a binary-format image represented by a facsimile image systematically on a pixel-by-pixel basis depending on a scaling factor causes various inconveniences. More specifically, the inconveniences are pronounced when reducing the data such that performing a thinning-out process on the data systematically in a simple manner may cause a dropout in the image with respect to a fine line, etc., such as a ruled line, a line within a character, and an underline, etc. Thus, the process may cause dropout of the character and difficulty in identifying the character, and loss of the ruled line or the underline. Therefore, various measures have been proposed up to now, especially on a method of reducing.
Patent Document 1
JP5-250468A
Patent Document 2
JP10-341335A
In the invention as described in the Patent Document 1, providing means for converting one pixel of an original image into one pixel of a reduced image when the integer part of the outcome of a multiplication is zero, and means for, when the negative value of the decimal part obtained by converting into the one pixel of the reduced image exceeds a predetermined value, not converting the one pixel of the original image into the reduced image, aims to reduce to the minimum level a crushing or a deformation in reducing an original image such that alternating black and white appears. However, this method is considered to be insufficient, as the original image is limited to a runlength of one pixel, and also from the point of view of keeping a black runlength which is generally an important information item in a binary format image.
Moreover, in the invention as described in the Patent Document 2, a method is proposed such that image data corresponding to one line for one direction are multiplied by a scaling factor per runlength so as to obtain scaled runlengths, and the decimal part of each of the scaled runlengths is truncated in the ascending order of the magnitude of the decimal part as described above in order to match the number of dots in one line after scaling so as to produce a scaled image, at which time as an exceptional process, the truncating as described above is postponed when the integer part of the scaled runlength is zero; and when even such postponing does not result in a sufficient reducing, the decimal part as described above is eliminated from a white dot.
According to this method, while an occurrence of a runlength (with the integer part of zero) disappearing by reducing may be avoided, final reduced-image data cannot be produced until a runlength-reducing operation for the whole one line has been completed. A buffer memory having a capacity corresponding to one line is required for collating the integer part and the decimal part of each runlength so as to store the collated parts. This may become not only an obstacle when trying to implement a scaling process with a small amount of memory resources, but, also when the process itself is implemented in software by means of a CPU, a burden on the CPU. Thus, in a method of operation for reducing, per runlength, binary format image data corresponding to one line, enabling real-time computing of reduced data with a relatively simple sequential process, and enabling keeping of important information on the image by not causing a loss of a small black runlength, are preferable.